Structural bearings

ABSTRACT

A structural bearing such as is employed in bridges and large buildings comprises a relatively thin layer of an elastomer, such as polyurethane, interposed between and bonded to two flat bearing members; at least one shear-resisting member, such as a pin passing through the elastomer layer, or a plate having its edge engaged with a ring surrounding the layer, extends between the two members and is in shear-resisting pivotal engagement with one of them in a manner to accommodate vertical compression of the elastomer and tilting of the two members. Other relative movements of the structure engaging the bearings are accommodated by relatively sliding parts thereof.

United States Patent [191 Fyfe [ STRUCTURAL BEARINGS [75] lnventorfEdward R. Fyfe, Burlington,

Ontario, Canada [73] Assignee: Elastometal Limited, Burlington,

Ontario, Canada 22 Filed: Apr. 27, 1971 21 Appl. No.: 137,896

Related US. Application Data [63] Continuation-impart of Ser. No.27,700, April 13,

1970, abandoned.

[52] US. Cl. 14/16, 308/238 [51] Int. Cl. E0ld 19/06 [58] Field ofSearch 14/16; 161/44; 308/238, 308/3; 248/22, 23

[56] References Cited UNITED STATES PATENTS 2,91 1,207 11/1959 Coble248/22 X 3,504,902 4/1970 Irwin 308/2R X 3,398,998 8/1968 Burnett 14/16X 3,397,856 8/1968 Sullivan 14/16 X 2,705,928 4/1955 Pont 14/16 X809,071 l/1906 Motley.... 14/16 2,680,259 6/1954 Milk 14/16 3,243,2363/1966 Graham..... 14/16 X 3,349,418 10/1967 Hein 14/16 [451 Apr. 30,1974 Delforce 14/16 X Primary Examiner-Nile C. Byers, Jr. Attorney,Agent, or Firm-Stanley J. Rogers [57] ABSTRACT A structural bearing suchas is employed in bridges and large buildings comprises a relativelythin layer of an elastomer, such as polyurethane, interposed between andbonded to two flat bearing members; at least one shear-resisting member,such as a pin passing through the elastomer layer, or a plate having itsedge engaged with a ring surrounding the layer, extends between the twomembers and is in shear-resisting pivotal engagement with one of them ina manner to accommodate vertical compression of the elastomer andtilting of the two members. Other relative movements of the structureengaging the bearings are accommodated by relatively sliding partsthereof.

5 Claims, 5 Drawing Figures vmmnmmw mm 18306375 sum 1 UF 2 INVENTOR.EDWARD R. FYFE I PATENTEDAPR 30 19M 3 8 06375 SHEET 2 BF 2 FIG5 T EDWARDR. FYFE I N VEN TOR.

BYM/w- STRUCTURAL BEARINGS CROSS-REFERENCE TO RELATED APPLICATION andnow abarfibfidi FIELD OF THE INVENTION The invention is concerned withimprovements in or relating to structural bearings, such as are employedfor example in bridges and large buildings to support the static anddynamic loads of the structure, while permitting some relative movementof the parts of the structure between which the bearing is disposed.

BACKGROUND OF THE INVENTION Structural bearing pads of the kindspecified generally comprise a body of elastomeric material havingreinforcing material incorporated therein, such as metal plates disposedwith their flat faces generally parallel to the top and bottom faces ofthe bearing pad.

Generally, such bearings are loaded horizontally and vertically. Thevertical load comprises the dead weight of the supported structure andany live load on the structure, and this load acts perpendicularly tothe top and bottom surfaces of the bearings and is carried by theelastomeric material which is thus subjected 'to compression. Thehorizontal load is due to movement of the supported structure caused bythermal expansion and contraction and this deflects the top surface ofthe bearing laterally with respect to the bottom surface, so that thebearing is loaded in shear.

The size of the bearing will largely depend on the magnitude of the loadto be carried. The horizontal cross-sectional area will be selectedaccording to the maximum vertical load to be carried by the bearing andthe loading capacity of the elastomeric material. The vertical height ofthe bearing will depend, among other factors, upon the verticalthickness of the elastomeric material, which is in turn dependent atleast in part upon the maximum tilt to which the bearing may besubjected, and-the need to ensure that the elastomer is not subjected totension under the maximum degree of tilting. The thickness of theelastomer will also be selected so that the required tilting andhorizontal deflection can be accommodated by the bearing withoutoverstraining in shear.

Structural engineers are developing and have developed bridge andbuilding designs that place increasing demands upon such bearings,requiring them to accommodate increasing loads without increase of sizeand cost, and preferably of course with decrease of both size and cost.For example, the known bearings employing one or more open layers ofneoprene elastomer have only been used for bridges of relatively shortspan fiup to bQB iQQ. ss l. .A earin QEHS$1F longerspans has requiredthe neoprene to be completely enclosed, comprising the so-called,relatively expensive pot bearing, because of the high stresses to whichit is subjected. Bridges of up to l ,600 feet span are now common, andit is to be expected that this trend will continue. There is also anaccompanying tendency to reduce the cross-section of the supportingcolumns as much as possible, so that the situation cannot be met simplyby increasing the size of the bearing.

If the horizontal size of the bearing is reduced by use of elastomericmaterials capable of higher loading, then because of the shear forcesapplied to the bearing, as described above, a much thicker layer must beused, and the bearing consequently is much thicker. Problems are alsoencountered in ensuringa mechanical bond between the elastomer and theother partsof the bearing that will withstand the maximum shear stressesapplied thereto.

DEFINITION OF THE INVENTION It is an object of the present invention toprovide a new structural bearing.

It is another object to provide a new bearing employing at least oneunrestrained layer of elastomeric material and of simple, inexpensiveconstruction.

In accordance with the present invention there is provided a structuralbearing comprising a supporting bearing member for engagement with astructure to be supported by the bearing, at least one layer ofelastomeric material interposed between the said supporting bearingmember and a support for the bearing when the bearing is in operativeposition on the support, characterised by the provision of at least oneco-operating bearing member capable of shear-resisting pivotalengagement with the said supporting bearing member to permit compressionof the elastomer layer and tilting of the supporting bearing memberrelative to the bearing v support under load, the shear-resistingbearing member being adapted for shear-resisting engagement with thesaid bearing support.

The said co-operating bearing member may comprise a pin passing throughthe said elastomeric material and having one end in pivotalshear-resisting engagement with the supporting bearing member.

The end of the said pin in engagement with the bearing supporting memberis of spherical segment external shape slidably engaged in a cylindricalbore in the bearing member coaxial with the pin, or alternatively theremay be provided a collar of complementary internal shape embracing thepin end, the collar exterior being cylindrical and the collar beingslidably engaged in a cylindrical bore in the bearing member coaxialwith the collar exterior and the pin.

Alternatively, the said supporting and shear-resisting bearing membermay comprise plate-like portions on opposite sides of the elastomerlayer, one of the bearing members having a surface thereof capable ofsaid shear-resisting engagement with an adjacent surface of the othermember, which adjacent surface extends toward the said one member andsurrounds its first mentioned surface.

The said shear-resisting engagement may take place upon the applicationto the bearing of from 50 percent to 75 percent of its maximum designedshear load.

DESCRIPTION OF THE DRAWINGS Particular preferred embodiments of theinvention will now be described, by way of example, with reference tothe accompanying diagrammatic drawings, wherein:

FIG. 1 is a front or rear elevation showing abearing in accordance withthe invention applied in support of a bridge structure, and

FIGS. 2 to 5 are transverse cross-sections through different embodimentsof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a typicalapplication of a bearing in accordance with this invention to thesupport of a bridge member on top of a single, slender, vertical column11, the bearing being indicated generally by the reference 12.

Referring more specifically to FIG. 2, the bearing illustrated thereincomprises two spaced, flat, circular plates 13 and 14 having a single,open-sided, uniform, flat cylindrical layer 15 of an elastomericmaterial interposed between the plates and bonded thereto by anysuitable treatment. A massive, solid, shear-resisting pin 16 coaxialwith the two plates and the elastomer layer extends between the plates,and transmits any shear force applied to the plate 13 directly to theplate 14, and vice versa, without permitting application of the force tothe elastomer layer.

In this embodiment the pin 16 is rigidly connected to the plate 14 bybeing formed integral therewith, while its end engaging the other plate13 has the external shape of a spherical segment, which is engaged forvertical sliding movement in a cylindrical bore 17 in the plate 13coaxial with the pin. The vertical sliding of the pin end in the borepermits the plates to move towards and away from one another, as thethickness of the elastomer layer varies with the applied load, while thepivotal engagement permits relative tilting of the two plates as thesupported structure moves on the bearing.

The lower plate 14 is fastened securely to the supporting column 11 inany suitable manner. Since the column illustrated in FIG. 1 is ofconcrete the plate is provided with downwardly extending anchor pins 18of conventional form. An inverted U-shape member 19 is similarlyconnected to the bridge member 10, being provided with upwardlyextending anchor pins 20. The facing surfaces 19a and 13a of the member19 and plate 13 respectively have a layer 21 of low-friction plasticmaterial (e.g., the material sold by DuPont under the Trade Mark Teflon)interposed between them, so that they may slide easily relative to oneanother to accommodate the corresponding movement of the bridge on thebearing. The surface of the layer 21 engaging the surface 19a isprovided with a large number of shallow recesses 22, each of whichcontains a suitable lubricant material to reduce the sliding friction.The edges of the plate 13 coextensive with downwardly extending portions19b of the member 19 are provided with layers 23 of low-frictionmaterial to reduce the sliding friction therebetween.

The preferred material for the elastomer layer 15 is a-polyurethane and,for example, such a material can accommodate a loading of say 2,000p.s.i., as compared with a loading of about 800 p.s.i. for neoprene. Asa practical example a bearing to withstand a 200 ton load must be ofabout 26 inches diameter with neoprene, but can be of about 16 inchesdiameter with polyurethane. Moreover, because of the presence of the pin60 substantially no shear forces can be applied to the elastomer layer,and its thickness need only be sufficient to accommodate the tiltingpermitted by the pivotal engagement of the pin with the plate 13. Thetilting that is likely to be obtained with any structure can readily becalculated as an angle, and the limitation is that the thickness must besufficient to ensure that the stretched part of the elastomer layerremains in compression and does not become under tension. In thepractical example referred to above the elastomer layer need only beabout one inch thick, whereas a prior art neoprene bearing would requirethe layer to be perhaps four inches thick to accommodate the anticipatedshear forces. Also, the bonds between the layer 15 and the plates 13 and14 are not subjected to any appreciable shear forces, so thatlimitations otherwise imposed by the possible failure of these bonds areavoided; it is found in general that higher strength elastomers such asthe polyurethanes are relatively difficult to bond to metals.

In the embodiment illustrated by FIG. 3 the shear resisting pivotalconnection of the pin 16 with the bearing member 13 is by means of acylindrical collar 24, which has an inner cylindrical surfacecomplementary to that of the end of the pin and closely embraces the pinend. The collar has an external cylindrical surface which is a closesliding fit in the cylindrical bore 17, so that the collar can slidetherein to accommodate changes in the thickness of the elastomer layerwith load. .The embodiments described can of course be inverted.

In all of the embodiments described the connection of the pin 16 withthe plate 13 accommodates both tilting movements and vertical movementsof the plate 13, since this structurally is the preferred arrangement.However, for example, in the embodiments of FIGS. 2 and 3 it would alsobe possible for the connection of the pin with the plate 13 toaccommodate tilting, while the connection with the plate 14 accommodatesvertical movements, the pin being vertically slidable in a suitablebore.

In the embodiment of FIG. 4 the inverted U-shaped member 19 of thepreceding embodiments that is illustrated as an integral unit is insteadformed in separate parts consituted by a plate 19, another plate 25carrying the anchor pins 20 which are removable, and side bar members26, the said separate parts being held together by bolts 27. The plate14 is provided with removable pins 18. Such a construction permits thebearing to be disassembled for removal and/or maintenance, etc. A thinlayer 28 of a material having an especially low coefiicient of frictionwith the material of the layer21 is clamped to the face of the plate 19that engages the layer 21; a particularly suitable material is a sheetof polished stainless steel, the use of such a sheet also avoiding theneed to polish or accurately machine the corresponding face of plate 19.

The end of the pin 16 projecting beyond the plate 14 is engaged in aco-operating housing 29 fixed to the plate 13, and the cylindrical bore17 in the housing is of a predetermined greater diameter than that ofthe pin 16, so that some shear force may be applied to the elastomerlayer 15 before the shear-resisting pin member and the housing 29 moveinto shear-resisting engagement with one another. Preferably, the amountof shear accommodated by the elastomer layer before such engagementtakes place is about 50 percent, and may be up to about percent, of themaximum designed shear load of the bearing, the remainder, if everapplied, being accommodated by the shear-resisting pin and housingconnection. Such a construction is preferred in some applications andenables a pin 16 of smaller diameter to be used, as compared with thepreviously described embodiments.

In the embodiment of FIG. 5 the pin 16 effectively becomes merged withthe plate 14, which is circular in plan, so that the plate 14 may beregarded as the mechanical equivalent of the pin. The plate is providedwith an edge face 14a, shaped like the corresponding face of the pin 16,and co-operating with an internal circular cylindrical face 29a of aring-like member 29 fixed to the edge of the plate 13, which is alsocircular in plan. The outer face of the member 29 is rectangular in planand carries the low-friction members 23 which engage the side bars 26,as with the embodiments described above. The ring 29 could alternativelybe fastened to the plate 14 and be extended toward the plate 13 so as tobe capable of pivotal engagement with the plate 13 to resist shearforces. The faces 14a are shown curved convex, as is preferred, butalternatively, or in addition, the co-operating face 29a surrounding thesurface 14a may be curved concave. It will be noted that although theelastomer is surrounded by the plates 13 and 14 and the circular face29a it is not physically restrained thereby.

The structure characterising the embodiments of the invention can beapplied to other forms of bearing, e.g., a floating" bearing notrequiring the side restraint provided by the bars 26. Other variationsof the embodiments described are of course possible within the scope ofthe claims and will be apparent to those skilled in the art.

I claim:

1. A structural bearing subjected to loads having both vertical andhorizontal components comprising, a first support member for mountingupon a structure on which the bearing is supported, an unenclosed layerof elastomeric material mounted on top of the first support member andbonded thereto, a second support member for operative enegagement with astructure supported by the bearing mounted on top of the layer ofelastomeric material and bonded thereto, and mechanical connecting meansextending between the support members through the layer of elastomericmaterial and mechanically connecting the support members to one another,the said connecting means comprising a pin fixed rigidly at one end tothe centre of one support member, passing vertically centrally throughthe said elastomer layer, and having its other end of spherical segmentexternal shape slidably engaged in a centrallydisposed, verticalcylindrical bore in the other support member coaxial with the pin, saidconnecting means permitting movement of the support members toward eachother upon compression of the layer of elastomeric material undervertical load components with vertical movement of the said other pinend in the bore, permitting tilting of the support members relative toeach other under corresponding components with rotation of the saidother pin end in the bore, and preventing transverse movement of thesupport members relative to each other under horizontal load componentsof greater than a predetermined extent by engagement of the said otherpin end with the wall of the bore to prevent the application to theelastomer layer of shear force of greater than a corresponding value.

2. A bearing as claimed in claim 1, wherein there is provided a collarembracing thepin other end and of internal shape complementary to thatof the embraced pin end, the collar exterior being of cylindrical shapecoaxial withthe pin and the collar being slidably engaged in the saidcylindrical bore in the other support member.

3. A bearing as claimed in claim 1, characterized in thatshear-resisting engagement takes place between the said other pin endand the wall of the bore upon the application to the bearing of from 50percent to percent of its maximum shear load.

4. A structural bearing subjected to loads having both vertical andhorizontal components comprising, a first circular plate-like supportmember for mounting upon a structure on which the bearing is supported,an unenclosed layer of elastomeric material mounted on top of the firstsupport member and bonded thereto, a second circular plate-like supportmember for operative engagement with a structure supported by thebearing mounted on top of the layer of elastomeric material and bondedthereto, and mechanical connecting means extending between the supportmembers around the layer of elastomeric material and mechanicallyconnecting the support members to one another, the said connecting meanscomprising a circular collar-like member fixed rigidly to one of thesupport members and having a surface thereof extending to the othersupport member and surrounding a co-operating outwardly convex circularsurface of the other support member, said connecting means permittingmovement of the'support members toward each other upon compression ofthe layer of elastomeric material under vertical load components withvertical movement of the other support member within the collar-likemember, permitting tilting of the support members relative to each otherunder corresponding components with rotation of the said other supportmember in the collar-like member, and preventing transverse movement ofthe support members relative to each other under horizontal loadcomponents of greater than a predetermined extent by engagement of thesaid other support member with the collar-like member to prevent theapplication to the elastomer layer of shear force of greater than acorresponding value.

5. A bearing as claimed in claim 4, characterized in thatshear-resisting engagement takes place between the cooperating surfacesof the collar-like member and the other support member upon theapplication to the bearing of from 50 percent to 75 percent of itsmaximum shear load.

1. A structural bearing subjected to loads having both vertical andhorizontal components comprising, a first support member for mountingupon a structure on which the bearing is supported, an unenclosed layerof elastomeric material mounted on top of the first support member andbonded thereto, a second support member for operative enegagement with astructure supported by the bearing mounted on top of the layer ofelastomeric material and bonded thereto, and mechanical connecting meansextending between the support members through the layer of elastomericmaterial and mechanically connecting the support members to one another,the said connecting means comprising a pin fixed rigidly at one end tothe centre of one support member, passing vertically centrally throughthe said elastomer layer, and having its other end of spherical segmentexternal shape slidably engaged in a centrallydisposed, verticalcylindrical bore in the other support member coaxial with the pin, saidconnecting means permitting movement of the support members toward eachother upon compression of the layer of elastomeric material undervertical load components with vertical movement of the said other pinend in the bore, permitting tilting of the support members relative toeach other under corresponding components with rotation of the saidother pin end in the bore, and preventing transverse movement of thesupport members relative to each other under horizontal load componentsof greater than a predetermined extent by engagement of the said otherpin end with the wall of the bore to prevent the application to theelastomer layer of shear force of greater than a corresponding value. 2.A bearing as claimed in claim 1, wherein there is provided a collarembracing the pin other end and of internal shape complementary to thatof the embraced pin end, the collar exterior being of cylindrical shapecoaxial with the pin and the collar being slidably engaged in the saidcylindrical bore in the other support member.
 3. A bearing as claimed inclaim 1, characterized in that shear-resisting engagement takes placebetween the said other pin end and the wall of the bore upon theapplication to the bearing of from 50 percent to 75 percent of itsmaximum shear load.
 4. A structural bearing subjected to loads havingboth vertical and horizontal components comprising, a first circularplate-like support member for mounting upon a structure on which thebearing is supported, an unenclosed layer of elastomeric materialmounted on top of the first support member and bonded thereto, a secondcircular plate-like support member for operative engagement with astructure supported by the bearing mounted on top of the layer ofelastomeric material and bonded thereto, and mechanical connecting meansextending between the support members around the layer of elastomericmaterial and mechanically connecting the support members to one another,the said connecting means comprising a circular collar-like member fixedrigidly to one of the support members and having a surface thereofextending to the other support member and surrounding a co-operatingoutwardly convex circular surface of the other support member, saidconnecting means permitting movement of the support members toward eachother upon compression of the layer of elastomeric material undervertical load components with vertical movement of the other supportmember within the collar-like member, permitting tilting of the supportmembers relative to each other under corresponding components withrotation of the said other support member in the collar-like member, andpreventing transverse movement of the suPport members relative to eachother under horizontal load components of greater than a predeterminedextent by engagement of the said other support member with thecollar-like member to prevent the application to the elastomer layer ofshear force of greater than a corresponding value.
 5. A bearing asclaimed in claim 4, characterized in that shear-resisting engagementtakes place between the cooperating surfaces of the collar-like memberand the other support member upon the application to the bearing of from50 percent to 75 percent of its maximum shear load.